Follow path Constraint, relative locations for offset objects
One approach, (I don't know whether it's the snappiest, or most controllable)


Copy the entire rig, track and trucks
On the copy, delete all trucks except the copy of the one you want to remain stationary in world space.. 'Target Truck'... ( red in the illustration )
Put a Copy Location constraint on the original track, targeted on 'Target Truck', World space, X,Y and Z, all inverted in the constraint.